Waste disposal systems in commercial aircraft typically employ vacuum-type flushing systems to forcibly transfer lavatory waste to a waste holding tank. The interior walls of the holding tank carry sensors that are activated when the level of waste rises to the maximum capacity of the tank. The sensors provide a signal to the flight crew that the tank is filled. The lavatory is then closed until the holding tank is emptied.
Often the waste will be drawn into the waste holding tank with such force that it is sprayed or splashed against the tank walls, thereby coating the sensors. The coated sensors are thus prematurely activated by the sprayed or splashed waste before the actual level of the waste reaches the sensors. This premature activation of the sensors results in needless and often inconvenient shutdown of the lavatory before the holding tank is actually filled.
One method of preventing the premature activation of the waste holding tank sensors is to apply a periodic spray of water against the sides of the tank to remove any accumulated matter on the sensors. This method involves the positioning of a sprayer head within the waste holding tank. The sprayer head is connected to a source of pressurized rinse water. The rinse water often carries foreign matter (such as rust particles) that tends to clog the sprayer head. It is therefore desirable to utilize sprayer heads with effective self-cleaning capabilities to eliminate the task of unclogging the somewhat inaccessible sprayer head by hand.
The prior art is replete with designs for self-cleaning shower or sprayer heads. The prior art devices, such as those shown in Filliung et al. (U.S. Pat. Nos. 2,770,497, Automatically Self-Cleaning Shower Heads) and Shames et al. (2,936,958, Self-Cleaning Shower Head), typically include a substantially cylindrical body that attaches to a water pipe that delivers water under pressure from a suitable source. The outlet end of the body has an inwardly projecting annular lip. The body houses a movable piston-like member that is mounted in the body by a spring or other elastic element. The piston-like member carries a disc on its outermost end. The space between the edge of the disc and the annular lip defines an outlet gap through which the water passes. The spring holds the disc away from the outlet end of the body when the water is shut off. When the water is supplied to the sprayer head, it forces the piston toward the outlet end of the body so that the gap between the disc and lip narrows. The narrow gap constricts the flow of water, thereby forming a spray. The self-cleaning aspect arises when the water is shut off and the piston and disc are retracted by the elastic member from the outlet end of the body. As the piston retracts, the outlet gap widens. Thus, any particles in the water that were restricted from passing through the gap during spraying are flushed through the now relatively wide gap by the water remaining in the sprayer head after the water is shut off.
Since the flushing action of prior art sprayer heads is accomplished by the water remaining in the sprayer head and adjacent section of pipe after the water supply is shut off, the flushing water provides no significant sprayer head cleaning force. Nor is any significant spray head cleaning force provided when the water is again turned on, since the water that is forced into the sprayer head by the source immediately moves the piston-like member to reduce the width of the gap. Therefore, with the prior art devices, flushing is never accomplished under conditions when the gap is at its widest and when the water flowing through the gap carries the flow energy imparted by the source. As a result, some of the particles, in particular those with widths roughly the same or slightly larger than the gap at its widest, remain in the sprayer head since they are never forced through the gap when the gap is at its widest by water having significant flow energy.